catalytic converter missing

PurpleSnow · Post by **PurpleSnow** » 30 Aug 2018, 03:51

Hi there guys

my 94 850 does not have a cat in but the O2 sensor is there. Im not a real expert on these cars or on cats in general but shouldnt I have a cat with the O2 sesnor into the cat.

Im having problems with high fuel consumption.

Post by **misha** » 30 Aug 2018, 04:00

No...o2 sensor is between flexi pipe and cat screwed into the exhaust pipe.
'94 should have only front(1st 02 sensor).
Late '96 & '97 have 2...2nd one is after the cat.
High fuel consumption could be everything....from vacuum leak to some bad sensors.
Check engine light on?
'94 produce flash codes and OBDI diagnostic ports are under the hood.
All you need is a piece of paper and pencil to write them down.

PurpleSnow · Post by **PurpleSnow** » 30 Aug 2018, 04:21

ok so my question then is if I dont have a cat. i bought the car as is. think they decat but suppose they didnt install a mini cat. would that be one of my problems

Post by **misha** » 30 Aug 2018, 05:14

With only one (front o2 sensor)....there is no problem for driving the car without the cat...only emissions can affect.
Fuel consumption would not be affected.

Post by **abscate** » 30 Aug 2018, 06:42

Even with two OXS a missing cat won't change fuel economy, at least with ME7

The rear OXS sensor just monitors, with no feedback to the fuel injection.

If the CAT is plugged, that could cause a performance change.

Post by **misha** » 30 Aug 2018, 06:54

On M4.4 cars BOTH of them are used for fine tuning the mixture(air & fuel)...some M4.3 cars have them both...depending on market.
They communicate to each other all the time.
I don't know about ME7.

Post by **mrbrian200** » 30 Aug 2018, 10:31

This is just me quizzing those who might be more knowledgeable about this - I am aware that under certain conditions the ECU will alter AFR in an attempt to protect the cat and/or exhaust valves from heat damage. The downstream sensor is not in any way involved in this calculation? Are we sure about this? In addition to monitoring overall efficiency, the difference between the upstream and downstream sensor could also be entered into a complex calculation to gauge how much unburnt fuel is being burnt off inside the cat. Which I believe should correlate with temperature even though cat temp isn't directly probed by a sensor, the ECU might be able to 'estimate' what the cat temp is and adjust AFR to keep things 'safe'.

OP, not having a downstream sensor on his year/model, doesn't need to worry about this.

Post by **Ozark Lee** » 30 Aug 2018, 13:45

On a '94 it has the Jetronic LH3.2 system in the US spec cars but in South Africa I don't know for sure. There is a Fenix ECU on some of the European spec cars and I know absolutely nothing about that setup.

On the Jetronic, as was said, there is only the upstream sensor and the lack of a catalytic converter makes no difference. One the exhaust passes that sensor the ECU has no way of determining what what happens. If there is wiring for a rear sensor and it is gone it will definitely throw a code for it since there is no current to the heater.

The flash codes are read from ports A-2 and A-6 on the LH3.2 setup and if you can pull the codes and post them back we can help. There can be error codes even if the lambda light isn't on.

The factory service manual has a great primer on reading and interpreting the codes. For a non turbo the appropriate document is the "Tests with Codes.pdf" file.

You can get a copy of the manual here:

https://www.matthewsvolvosite.com/downlo ... vo_850.zip

If you have a bunch of codes go ahead and record them and then clear them. After driving again recheck and see which ones come back. Codes stay set pretty much forever unless they are cleared so some could be "legacy" codes for problems that have since been corrected.

...Lee

Post by **misha** » 30 Aug 2018, 15:03

Siemens Fenix is in 10v cars Lee.